package com.shm.leetcode.concurrent;
/**
 * @author: shm
 * @dateTime: 2020/10/16 16:59
 * @description: 解题思路：
 * 这是一个典型的执行屏障的问题，可以通过构造屏障来实现。
 *
 * 如下图，我们需要构造 22 道屏障，second 线程等待 first 屏障，third 线程等待 second 屏障。：
 *
 *
 * first 线程会释放 first 屏障，而 second 线程会释放 second 屏障。
 *
 * Java 中，我们使用线程等待的方式实现执行屏障，使用释放线程等待的方式实现屏障消除。
 *
 * 我们使用一个 Ojbect 对象 lock 实现所有执行屏障的锁对象，两个布尔型对象 firstFinished，secondFinished 保存屏障消除的条件。
 *
 * 作者：pulsaryu
 * 链接：https://leetcode-cn.com/problems/print-in-order/solution/gou-zao-zhi-xing-ping-zhang-shi-xian-by-pulsaryu/
 */
class Foo1 {

    private boolean firstFinished;
    private boolean secondFinished;
    private Object lock = new Object();

    public Foo1() {
        
    }

    public void first(Runnable printFirst) throws InterruptedException {
        
        synchronized (lock) {
            // printFirst.run() outputs "first". Do not change or remove this line.
            printFirst.run();
            firstFinished = true;
            lock.notifyAll(); 
        }
    }

    public void second(Runnable printSecond) throws InterruptedException {
        
        synchronized (lock) {
            while (!firstFinished) {
                lock.wait();
            }
        
            // printSecond.run() outputs "second". Do not change or remove this line.
            printSecond.run();
            secondFinished = true;
            lock.notifyAll();
        }
    }

    public void third(Runnable printThird) throws InterruptedException {
        
        synchronized (lock) {
           while (!secondFinished) {
                lock.wait();
            }

            // printThird.run() outputs "third". Do not change or remove this line.
            printThird.run();
        } 
    }
}